Expression of CD31 on CLL or bystander cells does not influence survival and proliferation of CD38^high CLL cells. (A) Like ECRF24 and CD31-transfected 3T3-cells (3T31), CLL cells have a high surface expression of CD31, irrespective of CD38 expression (MFI-R = ratio mean fluorescence APC-conjugated CD31/ MFI APC-conjugated isotype-control; CLL CD38^low n = 8, CLL CD38^high n = 15; error bars represent SEM; n.s. = not significant, unpaired 2-sided Student t test). (B) There is no significant difference in viability of CLL cells cocultured with 3T3 and 3T31 cells, with or without addition of blocking CD31 antibodies (HEC65 and HEC170). CLL cells cocultured with 3T3 transfected with CD40-ligand (3T40L) have a significantly increased survival (viability shown at 5 days; * P < .05, paired 2-sided Student t test). (C) There is no significant modulation of viability of CLL-cells cocultured with 3T3 and 3T31 cells, with or without addition of the anti-CD38 antibody AT1 (viability shown at 5 days). (D) Combined CD40 and TLR-9 triggering induces marked proliferation of CLL cells.